Infectious Bronchitis (IB) is a viral respiratory disease that affects chickens and is caused by the coronavirus Infectious Bronchitis Virus (IBV). This disease is highly infectious and contagious and can affect chickens at any stage of their lives. However, young chicks, particularly those under six weeks of age, are more susceptible to the disease.
In addition to the respiratory system, IBV can also affect the oviduct and kidneys of chickens, causing further complications.
Infectious Bronchitis Management in Chicken
Causes of Infectious Bronchitis Disease
- Infectious Bronchitis (IB) is caused by the Infectious Bronchitis Virus (IBV), which belongs to the Corona group of viruses. IBV is a fragile virus and can be easily destroyed by common physical and chemical agents, including disinfectants and heat.
- The infection spreads through inhalation of droplets, ingesting contaminated feed and water, and contact with infected birds, contaminated equipment, clothing, and personnel. The virus is present in the respiratory discharges, feces, and eggshells of infected birds, making these a potential source of infection for healthy birds.
- The virus can survive well outside the bird’s body, particularly during winter. Therefore, the incidence and spread of the disease are often more common during the winter season. However, IB can occur in any season.
- The disease spreads rapidly in a flock, primarily through direct bird-to-bird transmission. The virus can also be transmitted through eggs, making vertical transmission possible. Fomites, such as equipment and clothing, can also transmit the virus.
Disease Cycle of Infectious Bronchitis
The disease cycle of Infectious Bronchitis (IB) typically involves the following stages:
- Incubation: After exposure to the virus, chickens enter an incubation period of 24-48 hours.
- Transmission: The virus spreads quickly between birds through direct contact or inhaling airborne virus particles.
- Replication: The virus replicates in the respiratory tract, particularly in the ciliated epithelial cells of the trachea and bronchi.
- Clinical signs: After the peak of virus excretion, clinical signs start to appear, such as respiratory signs (sneezing, coughing, gasping, etc.), conjunctivitis, and decreased egg production in laying hens.
- Recovery or death: The severity of the disease and outcome depends on various factors, such as the strain of the virus, the age and immune status of the chicken, and the presence of other infections. Mortality rates can range from negligible in adult birds to 25-60% in young chicks. Survivors may develop long-lasting immunity to the same strain of the IB virus, although new strains can cause disease.
- Shedding and reinfection: Recovered birds can shed the virus for several weeks after infection, leading to the reinfection of susceptible birds and contributing to the persistence of the disease in a flock.
Symptoms of Infectious Bronchitis Disease
Symptoms of Infectious Bronchitis Disease in chickens can vary depending on the age and type of bird affected. Some common symptoms include:
- Respiratory signs such as sneezing, coughing, gasping, tracheal rales, lachrymation, and nasal discharge
- Huddling under the hover
- Swelling of sinuses and face
- Mortality, which can be high in young chicks (up to 25%-60%)
- The course of the disease typically lasts 1-2 weeks in chicks.
- Respiratory noises that can be heard more distinctly at night
- Egg production declines rapidly in laying birds (5-50%)
- Damage to functional oviduct in adults, leading to egg abnormalities such as misshapen, thin or soft-shelled, rough, smaller, corrugated, and leathery eggs
- Poor egg quality with thin or watery white albumin
- Depression, ruffled feathers, wet droppings, and increased water intake in the uraemic form.
- Increased mortality (0.5-1% per week) due to urolithiasis (kidney stones) in uraemic form